Resectional surgery is a commonly applied practice in the field of orthopedics. Among other things, resectional surgery can be used to surgically treat orthopedic deformities or overgrowths in bone structures which may otherwise cause substantial discomfort and limit the range of motion in the affected region. A common complication involving such a deformity includes femoral acetabular impingement (FAI). An FAI is a condition in which movement of the hip joint is limited by an impingement between the acetabulum, or socket, of the pelvis and the head of the femur, or femoral head, pivotally attached thereto. Generally, the impingement may be caused by an overgrowth on an edge of the acetabulum, or pincer impingement, or by an overgrowth on the femoral head of the femur, or cam impingement. Both forms of impingement may be treated using resectional surgery to remove the overgrowth from the affected bones and to restore the full range of motion of the joint. With respect to cam impingement, for instance, an overgrowth on the femur may be resected to restore the sphericity of the femoral head and to enable the femoral head to pivot against the acetabulum without any impingement.
Although most impingement conditions may be successfully treated using currently existing surgical means, a substantial amount of detailed planning must precede the surgical procedure in order to ensure proper and efficient removal of the overgrowth. In cam impingement conditions, for instance, surgeons must pre-operatively determine a plan to recover or recreate the sphericity of the femoral head, and further, to ensure a smooth transition between the outer surfaces of the recreated femoral head and the femoral neck. Such planning involves at least the determination of the specific amount of femoral bone to be removed and the specific areas of the femoral head and neck from which the bone is to be removed. Currently, surgeons are capable of determining the degree of a particular cam impingement based on standard measurements taken from a medical image. More specifically, surgeons analyze and diagnose cam impingement conditions based on a relationship between the femoral head and neck, or an alpha angle, that is visually determined from images provided by an X-ray device, a computer tomography (CT) device, a magnetic resonance imaging (MRI) device, or the like. For example, based on the axial cross-sectional image typically taken through the center of the femoral head, as shown in FIG. 1, surgeons may define the alpha angle α as the angle measured between the neck axis NA of the femur and the line connecting the head center HC with a deviation point p. The head center HC is defined as the center of a circle or sphere S that approximates the femoral head. The neck axis NA is defined as the axis through the center of the femoral neck, or neck center NC, and the head center HC. The deviation point p is defined as the point where the outer surface of femoral head deviates from or exits the approximating sphere S.
By conventional standards, if the alpha angle is greater than 50-55°, a cam impingement may be diagnosed. This provides the surgeon with some standard measure with which to proceed. However, the surgeon is still left with less conventional means for determining the specific volume and areas of the femur that need to be removed during surgery. While advanced three-dimensional imaging devices and computer-aided surgical systems may provide some assistance during the stages of planning and performing surgery, the limitations in visibility and the lack of clear access to the pathologic joint introduce other setbacks. For instance, it may be difficult for the surgeon to visually plan or model the specific dimensions and locations of the resection volume based purely on a series of medical images. Even once a surgical plan is determined, there may still be difficulties in properly and efficiently communicating the specific dimensions and/or locations of the resection volume to a computer-aided system or a haptic- or robot-guided surgical device. Such difficulties and the lack of convention in planning for impingement surgery may place a significant burden on surgeons in the field, and further, may cause impingement surgery in general to be conducted inefficiently and inconsistently.
Accordingly, there is a need to streamline and further facilitate the planning process for surgical treatment of orthopedic impingement conditions. Moreover, there is a need for a computer-aided system or method which provides more conventional, more efficient and more accurate measures for modeling the resection volume prior to surgery.